Meeting the challenge of carbon capture: is CO2 capture a real problem in IGCC plants and are some issues being neglected?

Abstract

I have only recently been able to read the article in Energy Materials that summarised the meeting last year at Loughborough on ‘Energy materials: meeting the challenge’.1 Having recently fi nished working at the European Commission’s Institute of Energy in The Netherlands on an IGCC (integrated gasifi cation with combined cycle) type gasifi cation system to produce hydrogen from coal, and capture CO2, I was taken aback at what it appeared was being said about IGCC. Perhaps this was a result of the need to compress a lot information into a relatively small space, but after outlining pre-combustion processes, by which coal gasifi cation can be used to produce CO2 and hydrogen, the text continues: ‘However, the [energy] penalty is signifi cant: a plant that was 20% effi cient would use all of its energy to capture carbon.’ (emphasis added). This may be a general comment on all carbon capture plants, but a casual reading (by a Government Minister or an adviser?) could suggest that typical effi ciencies of IGCC, without carbon capture, are around 20%.The correct interpretation is that if one starts with any type of non-carbon capture plant that has an effi ciency of around 20%, the amount of CO2 that will be produced per megawatt hour is so high that all the energy in the plant will be needed simply to capture the CO2 and pump it up to pipeline pressure. In practice, no modern plant has an effi ciency as low as this. Even the old generating plant at Battersea (London) ran at 28%, and that was in the 1930s. More modern units are in the 43–46% range, depending on how advanced are the steam conditions However, the conjunction of these two passages of text could be taken to imply that pre-combustion processes are struggling. In addition, the whole tenor of the section on carbon capture and storage suggests that all these processes, whether based on conventional steam plant, oxyfuel, or IGCC, have problems in capturing carbon dioxide. Whatever can be stated about the potential challenges of capturing carbon dioxide from steam plant, oxyfuel or combined cycle gas turbines (CCGTs), it can be said with absolute certainty that CO2 removal is not a problem when using gasifi cation as an intermediate step to producing electricity. I can affi rm this from personal experience. Although I graduated as a metallurgist, my fi rst real job after leaving university was to run a steam reforming plant. Such processes, which used naphtha (basically unrefi ned petrol) to produce a hydrogen rich gas, were rapidly replacing the old fashioned gasworks of the time. They were cheap and simple to operate, even by metallurgists! Figure 1 shows the type of plant used by British Gas at that time. A critical aspect in steam reforming was removal of CO2 to improve the calorifi c value of the gas sent to consumers. Carbon dioxide was absorbed using potassium carbonate solution and released to atmosphere, along with some steam. If there had been the need there would have been absolutely no problem in compressing the CO2. Indeed for many years there have been coal and heavy oil plants, around the world, producing hydrogen for ammonia production, or hydrocracking, all of which have to remove the carbon dioxide to obtain the required hydrogen purity. The plant which I helped to run had a thermal output of about 200 MW, and would be regarded as minute compared modern units of the ammonia synthesis type. So the statement that there are problems in capturing CO2 in a pre-combustion process cannot be allowed to stand. 1 CO2 removal section of a steam reforming plant at Plymouth Gasworks in 1968: the tall towers are stripper columns for removing CO2 from the K2CO3 absorbent